In electrophotographic laser printers, there is known a laser printer in which process cartridges each including a photosensitive drum and a developing cartridge are detachably installed in an apparatus main body.
As a laser printer like this, there is proposed a laser printer in which a drum cover for opening and closing an opening from which a photosensitive drum is exposed is provided on a housing of a process cartridge in order to protect the photosensitive drum.
According to the above described laser printer, the drum cover is formed into a plate element having an arc-like cross section and extending along a circumferential surface of the photosensitive drum and covers the whole area of a portion of the photosensitive drum which is exposed from the opening. A circumferential end portion of the drum cover is supported rotatably on a shaft provided on the housing. In such a state that the process cartridge is detached from the apparatus main body, the opening is closed by the drum cover. When the process cartridge is installed into the apparatus main body, by being interlocked with this operation, the drum cover is caused to rotate about the shaft, whereby the opening is opened. By this action, the circumferential surface of the photosensitive drum is exposed from the opening, thereby making it possible to transfer an electrostatic latent image formed on the photosensitive drum onto a transfer sheet.